Field of the Invention
The present invention relates to optical subassemblies, particularly to hermetically sealed optical subassemblies.
Description of Related Art
There are many advantages of transmitting light signal via optical fiber waveguides and the use thereof is diverse. Single or multiple fiber waveguides may be used simply for transmitting visible light to a remote location. Complex telephony and data communication systems may transmit multiple specific optical signals. The data communication systems involve devices that couple fibers in an end-to-end relationship, including optoelectronic or photonic devices that include optical and electronic components that source, detect and/or control light, converting between light signals and electrical signals, to achieve high speed and high capacity data communication capabilities.
In an optical communication system, components on the transmission side are typically packaged in a transmitter optical subassembly (TOSA), and components on the receiving side are typically packaged in a receiver optical subassembly (ROSA). For bidirectional signal transmission along a single optical fiber, components are packaged in a bidirectional optical subassembly (BOSA).
Heretofore, the TOSA consists of a laser diode (e.g., a distributed feedback (DFB) laser), optical interface, monitor photodiode, metal and/or plastic housing, and electrical interface. Depending upon the required functionality and application, other components may be present as well including filter elements and isolators. It is used to convert an electrical signal into an optical signal that is coupled into an optical fiber. The ROSA consists of a photodiode, optical interface, metal and/or plastic housing, and electrical interface. Depending upon the required functionality and application, other components may be present as well including trans impedance amplifiers. It is used to receive an optical signal from a fiber and convert it back into an electrical signal. A BOSA consists of a TOSA, a ROSA and a WDM filter so that it can use bidirectional technology to support two wavelengths on each optical fiber.
For the TOSA, semiconductor lasers used in fiber optics industry are small, sensitive devices. They are typically a few hundred microns long, with tiny pads for cathode and anode that need wire bonding for electrical connection. It is generally necessary to strictly regulate the operating temperature of the laser in order to stabilize the wavelength of the light; this is typically done using a thermoelectric cooler (TEC). Moreover, to couple the light generated by them into an optical fiber, focusing lenses with tight alignment tolerances are needed. Because of these delicacies, proper packaging is a crucial aspect.
With the TOSA, an optical subassembly fulfills several functions. It provides a stable mechanical platform for the laser chip along with the necessary electrical interconnects. Inside the TOSA, the interconnects are wirebonded to the laser's cathode and anode. Practical TOSAs may include a number of other electronic parts, such as power monitoring diodes, TEC coolers, and external modulators. The laser diode (and any additional device) is mounted on a substrate.
In assembling a TOSA package, the laser is aligned with an optical fiber so as to provide sufficient coupling efficiency. The laser and the optical fiber may also need to be aligned with lenses disposed therebetween. It is often difficult and challenging to align all of the optical components to each other since three-dimensional alignment is typically required. In addition, for a variety of applications, it is desirable to hermetically seal the opto-electronic devices within the housing of the TOSA package, to protect the components from corrosive media, moisture and the like.
Heretofore, in a hermetically sealed package, the opto-electronic components (receiver and/or transmitter and associated optical elements and electronic hardware) are contained in an opto-electronic package. The optical fiber is introduced from outside the housing of the opto-electronic package, through an opening provided in the housing wall. The end of the optical fiber is optically coupled to the opto-electronic components held within the housing. A feedthrough element supports the portion of the optical fiber through the wall opening. Since the package of the opto-electronic package must be hermetically sealed as whole, the feedthrough element must be hermetically sealed, so that the electro-optic components within the opto-electronic package housing are reliably and continuously protected from the environment.
Heretofore, hermetic feedthrough is in the form of a cylindrical opening in the package housing defining a relatively large clearance through which a section of the optical fiber passes. A sealing material such as glass frit or metal solder is applied to seal the clearance space between the optical fiber and the housing. Given the large clearance between the housing and the optical fiber and the use of sealant material and its clearance (i.e., a layer of material between the external fiber wall and the inside wall of the housing), the housing does not support the optical fiber with precise positional alignment with respect to the components inside housing. The end of the optical fiber is required to be positioned by a ferrule or other alignment feature that is optically aligned with the opto-electronic components provided in the package. To optically couple the input/output of the optical fiber to the opto-electronic components in the package, optical elements such as lenses and mirrors are required to collimate and/or focus light from a light source (e.g., a laser) into the input end of the optical fiber (or to collimate and/or focus light from the output end of the optical fiber to the receiver). To achieve acceptable signal levels, the end of the optical fiber must be precisely aligned at high tolerance to the transmitters and receivers, so the optical fiber is precisely aligned to the optical elements supported with respect to the transmitters and/or receivers.
It can be appreciated that for a TOSA, the connection and optical alignment of the optical fiber with respect to a transmitter must be assembled and the components must be fabricated with sub-micron precision. In the past, it has been challenging for TOSAs to be economical produced in a fully automated, high-speed process. Similar challenges apply to ROSA and BOSA.
U.S. Patent Application Publication No. US2016/0274318A1, commonly assigned to the assignee of the present invention, discloses an optical bench subassembly including an integrated photonic device. Optical alignment of the photonic device with the optical bench can be performed outside of an optoelectronic package assembly before attaching thereto. The photonic device is attached to a base of the optical bench, with its optical input/output in optical alignment with the optical output/input of the optical bench. The optical bench supports an array of optical fibers in precise relationship to a structured reflective surface. The photonic device is mounted on a submount to be attached to the optical bench. The photonic device may be actively or passively aligned with the optical bench. After achieving optical alignment, the submount of the photonic device is fixedly attached to the base of the optical bench.
What is needed is an improved hermetic optical subassembly, which reduces package size, and improves manufacturability, throughput, optical alignment tolerance, ease of use, functionality and reliability at reduced costs. The present invention improves on the invention disclosed in U.S. Patent Application Publication No. US2016/0274318A1.